1. Field of the Invention
The present invention relates to a charged particle beam writing apparatus and a charged particle beam writing method. For example, the present invention relates to a writing method and apparatus that suppresses resist heating.
2. Description of Related Art
The microlithography technique which advances microminiaturization of semiconductor devices is extremely important as being a unique process whereby patterns are formed in the semiconductor manufacturing. In recent years, with high integration of LSI, the line width (critical dimension) required for semiconductor device circuits is decreasing year by year. In order to form a desired circuit pattern on semiconductor devices, a master or “original” pattern (also called a mask or a reticle) of high precision is needed. Thus, the electron beam writing technique, which intrinsically has excellent resolution, is used for producing such a highly precise master pattern.
FIG. 17 is a schematic diagram explaining operations of a variable-shaped electron beam (EB) writing apparatus. As shown in the figure, the variable-shaped electron beam writing apparatus operates as described below. A first aperture plate 410 has a quadrangular opening 411 for shaping an electron beam 330. A second aperture plate 420 has a variable-shape opening 421 for shaping the electron beam 330 having passed through the opening 411 of the first aperture plate 410 into a desired quadrangular shape. The electron beam 330 emitted from a charged particle source 430 and having passed through the opening 411 is deflected by a deflector to pass through a part of the variable-shape opening 421 of the second aperture plate 420, and thereby to irradiate a target workpiece or “sample” 340 placed on a stage which continuously moves in one predetermined direction (e.g. X direction) during the writing. In other words, a quadrangular shape that can pass through both the opening 411 and the variable-shape opening 421 is used for pattern writing in a writing region of the target workpiece 340 on the stage continuously moving in the X direction. This method of forming a given shape by letting beams pass through both the opening 411 of the first aperture plate 410 and the variable-shape opening 421 of the second aperture plate 420 is referred to as a variable shaped beam (VSB) method.
When performing the electron beam writing, the layout where a plurality of figures are densely arranged or figures are arranged to be overlapped with each other may be written. The case of slash patterns etc. can be cited as an example of the layout where figures are arranged to be overlapped with each other. By performing overlapping of figures, the number of shots can be reduced and the writing time can be shortened. When writing such layout figures as they are without any change, the dose density of the electron beam may be high. Therefore, there occurs a problem of being greatly affected by resist heating compared with a case of writing layout figures with sparse density. Thus, there is a problem that dimension etc. of a figure pattern written with such a high density may be varied.
As a method of reducing resist heating, for example, generally adopted is a multiple writing method of performing writing of patterns while overlapping them a plurality of times. As the multiple writing method, there are proposed a method of writing all the internal figure patterns a plurality of times by repeating the first writing and the second writing per unit of stripe region which is made by virtually dividing a chip region, and a method of writing all the internal figure patterns a plurality of times by alternately repeating the first writing and the second writing per unit of subfield in the stripe region (refer to, e.g., Japanese Patent Application Laid-open No. 2008-117871).
According to the multiple writing described above, a required dose is obtained by making one dose small for each figure and overlappingly writing the same figure a plurality of times. Further, it is also requested to overcome the problem by other method.